Fix empty upper limit range in histogram

[lafolle]

$ flen crypto/hmac
Full path of pkg:  /usr/local/go/src/crypto/hmac

[1-6)   -       ∎∎∎∎∎
[6-11)  -       ∎∎
[11-16) -       ∎
[16-21) -
$

Line with prefix "[16-21)" should not be present.